高电压设备测试（High Voltage Equipment Testing）（英文版） 课件 Worksheet 6 Insulating Oil Dielectric Strength Test

《HighVoltageEquipmentTesting》InsulatingOilDielectricStrengthTest主讲人：何发武（副教授）OperatingWorksheet：OperatingWorksheet：TableofContents01Followme02Workshop03Training01FollowmeⅠ.PrincipleofDielectricStrengthTestingforInsulatingOilDielectricstrengthtestingforinsulatingoilisacommonlyusedmethodtoassesstheinsulationperformanceoftheoil,anditisanimportantmeanstoevaluatetheinsulationpropertyofinsulatingoilasatypeofinsulationmaterial.Theinsulationperformanceofinsulatingoiliscrucialforthesafeoperationofelectricalequipment.Thedielectricstrengthtestforinsulatingoildeterminesitsabilitytowithstandvoltageunderhighelectricfields,therebydeterminingitssuitabilityforuseinhigh-voltageequipment.Ⅰ.PrincipleofDielectricStrengthTestingforInsulatingOilTheprincipleofdielectricstrengthtestingforinsulatingoilismainlybasedontheeffectofanelectricfield.Duringthetest,ahighvoltageisappliedtotheinsulatingoiltogenerateastrongelectricfield.Theinsulationperformanceoftheinsulatingoildeterminesitsabilitytowithstandvoltageunderanelectricfield,knownasthedielectricstrength.Duringthetest,twoelectrodesareinsertedintotheinsulatingoil,servingaspositiveandnegativeelectrodesrespectively,andahighvoltageisapplied.Theelectricfieldformedbetweentheelectrodeswillconductabreakdowntestontheinsulatingoiltoevaluateitsinsulationcapability.Ⅰ.PrincipleofDielectricStrengthTestingforInsulatingOilThereareseveralkeypointstonoteduringtheprocessofdielectricstrengthtestingforinsulatingoil.First,itisimportanttoensuregoodcontactbetweentheelectrodesandtheinsulatingoil,andthedistancebetweentheelectrodesshouldmeetthetestingrequirements.Second,itisimportanttoensuretheuniformdistributionoftheelectricfieldbetweentheelectrodesandtheinsulatingoil,toavoidlocalizedhighelectricfieldintensity.Additionally,theeffectoftemperatureshouldbeconsideredduringthetest,asthereisacertainrelationshipbetweenthedielectricstrengthoftheinsulatingoilandtemperature.Figure3-40showsanautomaticinsulatingoildielectricstrengthtester.Ⅰ.PrincipleofDielectricStrengthTestingforInsulatingOilFigure3-40

Automaticinsulatingoildielectricstrengthtester1–LCD;2–Functionkeys;3–Printer;4–Boostingrateswitch;5–Indicatorlight;6–Oilcupcompartmentcover;7–Temperatureandhumiditysensors;8–Groundlinecolumn;9–Powersocket;10–Powerswitch;11–Highvoltagesafetysign.Ⅱ.OverviewofInsulatingOilInsulatingoiliswidelyusedinhigh-voltageelectricalequipmentsuchastransformers,instrumenttransformers,switchgear,oil-filledcables,powercapacitors,andbushings.Duringoperation,theperformanceofinsulatingoilgraduallydeterioratesduetotheeffectsofoxygen,hightemperature,highhumidity,sunlight,strongelectricfields,andimpurities,whichpreventitfromfullyfunctioningasaninsulator.Ⅱ.OverviewofInsulatingOilInordertoconfirmwhethertheinsulationperformanceofinsulatingoilmeetstherequirements,regulartestsonitsrelevantpropertiesmustbeconducted.AccordingtothenationalstandardGB507–2002“MethodforTestingDielectricStrengthofInsulatingOil,”thedielectricstrengthofinsulatingoilreferstothebreakdownvoltage,breakdownstrength,andvoltagewithstandcapabilityoftheoil.Itisanimportantqualityindicatorthatrepresentstheabilityofinsulatingoiltowithstandvoltage.Thedielectricstrengthtestgraduallyincreasesthevoltageappliedtotheinsulatingoilunderspecifiedtestconditionsuntilitbreaksdownandlosesitsinsulationproperties.Itisexpressedastheaveragebreakdownvoltagedividedbytheelectrodedistance(kV/cm).Ahigherdielectricstrengthindicatesbetterinsulationperformance.Ⅱ.OverviewofInsulatingOilTransformeroilisafractionaldistillationproductofpetroleum,mainlycomposedofcompoundssuchasalkanes,cycloalkanes,saturatedhydrocarbons,andaromaticunsaturatedhydrocarbons.Itisamixtureofliquidnaturalhydrocarbonsobtainedfromthelubricatingoilfractioninpetroleumthroughacid-baserefining,whichispure,stable,haslowviscosity,goodinsulation,andcoolingproperties.Itisalightandyellowtransparentliquidwitharelativedensityof0.895andafreezingpointbelow-45C.Transformeroilservesasaninsulatingandcoolinglubricatingmediumintheoil-immersedtransformer.Theservicelifeoftransformeroilcanusuallyreach10–15years.Ⅱ.OverviewofInsulatingOil(Ⅰ)Requirementsforinsulatingoil(1)Itshouldhaveahighdielectricstrengthtoadapttodifferentoperatingvoltages.(2)Itshouldhavealowviscositytomeettheneedsofcirculationconvectionandheattransfer.(3)Itshouldhaveahighflashpointtemperaturetomeetfiresafetyrequirements.(4)Itshouldhavesufficientlow-temperatureperformancetowithstandpotentiallow-temperatureenvironments,andgoodoxidationresistancetoensurealongservicelifeoftheoil.Ⅱ.OverviewofInsulatingOil(Ⅱ)Electrical,physicalandchemicalpropertiesoftransformeroilJudgingthequalityofoilfromitsappearance,thecolorofnewoilisgenerallylightandyellow,butitturnsdarkredafteroxidation.Ifthecolorofoilbecomesdarkquicklyduringoperation,itindicatesthattheoilqualityhasdeteriorated.Normaltransformeroiliscolorlessandodorless.Ifthereisadifferentodor,itmeansthattheoilqualityhasdeteriorated(asshowninFigure3-41).Forexample,aburntsmellindicatesthattheoilhasoverheatedwhenitdriesout,anacidicsmellindicatesthattheoilhasseriouslyaged,andanacetylenesmellindicatesthatarcinghasoccurredwithintheoil.Newoilhasgoodtransparencyandistransparentinaglassbottlewithblue-violetfluorescence.Ifitlosesitsfluorescenceandtransparency,itindicatesthepresenceofwater,mechanicalimpurities,andfreecarbon.Ⅱ.OverviewofInsulatingOilFigure3-41

TransformeroilsamplesⅡ.OverviewofInsulatingOil(Ⅲ)Electrical,Physical,andChemicalPropertiesTestingofTransformerOilThebreakdownvoltageoftransformeroiliscloselyrelatedtothecleanlinessofnewoilandthedeteriorationconditionofoperatingoil.Theelectrical,physical,andchemicalpropertiestestingoftransformeroilareshowninTable3-22.Ⅱ.OverviewofInsulatingOilTable3-22

Electrical,Physical,andChemicalPropertiesTestingofTransformerOilⅡ.OverviewofInsulatingOilTable3-22

Electrical,Physical,andChemicalPropertiesTestingofTransformerOilⅢ.PerformanceofTransformerOilTransformeroilservesasamediumwithinelectricalequipmentandmustpossessgoodelectricalperformanceinordertofullyfunctionasinsulationandcooling.Themainelectricalperformancesofnewoilincludeinsulationstrengthanddielectricdissipationfactor.Ⅲ.PerformanceofTransformerOil(Ⅰ)InsulationStrengthInsulationstrengthreferstothedielectricstrengthorbreakdownvoltageoftransformeroil.Itmeasurestheabilityoftheoiltowithstandvoltagewithinelectricalequipmentwithoutbeingdamaged.Thisisoneofthemainmethodstoassessthequalityoftransformeroil.Thebreakdownprocessofinsulatingoilisrelatedtoitspurity.Pureinsulatingoilhashighbreakdownstrength(upto106

kV/cm),anditsbreakdownprocessismainlycausedbyelectricalbreakdown.Theoilinequipmentoftencontainsvariousimpurities,suchasgases,moisture,solidparticles,andpolymersgeneratedfromoilaging.Ⅲ.PerformanceofTransformerOil(Ⅱ)DielectriclossfactorThedielectriclossfactorprimarilyreflectsthepowerlosscausedbyleakagecurrentintheoil.Themagnitudeofthedielectriclossfactorissensitiveindeterminingthedegreeofdegradationandcontaminationoftransformeroil.Thedielectriclossfactorcanonlyindicatewhethertheoilcontainspollutantsandpolarimpurities,butitcannotdeterminethespecifictypeofimpuritiespresentintheoil.However,whentheoildeterioratesduetooxidationoroverheating,orwhenitismixedwithotherimpurities,thedielectriclossfactorincreasesasthecontentofimpuritiesorcolloidalsubstanceschargedintheoilincreases,evenuptomorethan10%.Ⅲ.PerformanceofTransformerOilDielectriclosstestsaremainlyusedtodeterminewhethertheoilisdirtyordegraded.Theycanonlydeterminethepresenceofpolarsubstancesintheoil,butnotthespecifictypeofpolarsubstances.Inthecaseoffurtheroxidation,theoil’sabilitytodissolvewatermayincrease,andthereforethepresenceofsludgeinthistypeofoilmaynotbereflectedinthedielectriclossfactor.Ifthedielectriclossexceeds0.7%,aninspectionisrequired.Ifthedielectriclossat100Cis7–10timeshigherthanthatat25C,itindicatesthattheoilisdirtyratherthancontainingmoisture.Ⅲ.PerformanceofTransformerOil(Ⅲ)PhysicalandChemicalPropertyTests(1)AppearanceandColorofOilGoodoilshouldbecleanandtransparent.Ifitisunclear,itmaycontainwater,carbonparticles,orsludge.Ifcarbonparticlesarefound,theremaybearcingorpartialdischargephenomenainsidethetransformer,anditisnecessarytoperformchromatographicanalysisontheoil.Ifthereisasignificantchangeinthecoloroftheoil,payattentiontowhethertheoilisagingacceleratedorthemonitoringoftheoperatingtemperatureoftheoil.Ⅲ.PerformanceofTransformerOil(2)AcidvalueAcidvaluereferstotheacidiccomponentscontainedin1goftestoil,expressedasmgKOH/g.Itisanimportantindicatorfortestingtransformeroilandreflectsthedegreeofoilrefinementandoxidation.Theincreaseinacidvalueisasignofinitialoildeterioration,andthepresenceofacidicsubstanceswillinevitablygeneratesludge.Ifthereismoistureintheoil,itcancauserustingofmetalssuchasironandalsodamagepaperinsulation.Ⅲ.PerformanceofTransformerOil(3)InterfacialtensiontestTheinterfacialtensiontestisquitesensitivetodegradationproductsintheoilandsolubleimpuritiesgeneratedfromsolidinsulationmaterials.Thegreaterthecontentofoxidationproductsintheoil,thelowertheinterfacialtension.Iftheinterfacialtensionvalueintheoilisbetween27–30mN/m,itindicatesatendencyforsludgeformation.Ifthetensionvaluedrops8mN/m,itindicatessevereoilagingandshouldbereplaced.Ⅲ.PerformanceofTransformerOil(4)MoistureContentMoistureintheoilandinsulationpaperreachesanequilibriumstate.Theoilhasdifferentsaturationlevelsofdissolvedmoistureatdifferenttemperatures.Thissaturationlevelincreaseswithtemperature,somoisturefromtheinsulationpaperenterstheoilathightemperatures.Whentheoiltemperaturedrops,someofthemoistureintheoilwilldiffuseintothepaper,causingadecreaseinthewatercontentintheoil.Ⅲ.PerformanceofTransformerOil(5)FlashpointTheflashpointisthelowesttemperatureatwhichthevaporofanoilmixturewithairwillignitemomentarilyuponcontactwithaflame,underspecifiedconditionsoftemperature,time,andflamesize.Thevolatilityoftheoilproductisactuallyrelatedtothesafetyoftransformeroilintheconditionsofuseandcanbemeasuredbytheflashpoint.Ⅲ.PerformanceofTransformerOilTheflashpointandignitionpointarenotequivalentconcepts.Theflashpointreferstothelowesttemperatureatwhichtheoilgasproducedissufficientandwhenanexternalflameisadded,theoilgasignitesmomentarily;theignitionpointisthelowesttemperatureatwhichanexternalflamecanbemaintainedfor5secondswhentheoilgascontinuouslyproducedbyheating.Thesampleisheatedataslowandconstantrateundercontinuousstirring.Atpredeterminedtemperatureintervals,asmallflameisintroducedintothecupwhilestirringisinterrupted.Theminimumtemperatureatwhichtheflamecausesthevaporonthespecimentoflashfireiscalledtheclosedflashpoint.Ⅲ.PerformanceofTransformerOil(6)Water-solubleacidWater-solubleacidreferstowater-solublemineralacids,primarilysulfuricacidanditsderivatives,thatareformedduringtheprocessingandstorageofoilproducts.Transformeroilgenerallyproduceslowmolecularweightorganicacids,suchasformicacidandaceticacid,duringtheprimaryoxidationstage.Theseacidshavegoodwatersolubility.Whenthewater-solubleacidcontentintheoilincreases(i.e.,thepHvaluedecreases)andthereiswaterpresentintheoil,itcancorrodesolidinsulationmaterialsandmetals,reducetheinsulationperformanceofelectricalequipment,andshortentheservicelifeoftheequipment.Shakethetestoilandanequalvolumeofdistilledwatervigorouslytomixthem.Extractthewaterphasefromthemixtureandaddanindicator.Observeanycolorchangestodeterminethepresenceofwater-solubleacidsandwater-solublealkalisinthetestoil.TheresultsarerepresentedbythepHvalue.Ⅳ.JudgmentstandardofoilqualityTable3-23

GB/T7595–2017

QualityStandardforIn-serviceTransformerOilⅣ.Judgmentstandardofoilquality02WorkshopⅠ.InsulatingOilDielectricStrengthTestStepsandPrecautionsWhenconductingadielectricstrengthtestoninsulatingoilusinganinsulatingoilwithstandvoltagetester,thefollowingprocedureshouldbefollowed:(1)Groundtheinstrumentreliably.(2)Whenthepowerisoff,placethemagnetometerintheoilcup.(3)The“sampleoil”mustbeplacedinthelaboratoryforaperiodoftimewithoutdamagingtheoriginalstorageseal,untiltheoiltemperatureisclosetoroomtemperaturebeforeuncoveringforthetest.Beforeuncovering,gentlyshakethetestoiltoevenlydistributeimpurities,butdonotproducebubbles.Beforethetest,washtheoilcup2–3timeswiththetestoil.Ⅰ.InsulatingOilDielectricStrengthTestStepsandPrecautions(4)Whenthesampleoilisloadedintotheoilcupinapower-offstate,itshouldflowdownslowlyalongtheinnerwalloftheoilcuptoreducebubbles.Duringoperation,itisnotallowedtotouchtheelectrodes,theinsideoftheoilcup,andthetestoilwithhands.Aftertheoilcupisfilledwithtestoil,itmustbeleftstillfor10–15minutesbeforestartingthebreakdowntest.(5)Inapower-offstate,covertheelectrodecoverandclosethehigh-voltagechamberlid.(6)Turnonthepowerswitch,andaftertheinstrumentdisplaysthewelcomescreen,itautomaticallyentersthemaininterface.(7)Usingthemouse,selectoperationssuchasbreakdowntest,withstandvoltagetest,viewhistoricaldata,timesetting,andPCcommunication.Ⅱ.Dielectricstrengthtestmethodforinsulatingoil(Ⅰ)Operationmethodforbreakdowntest(1)Setthetestparameters,includinginitialsettlingtime,numberoftests,settlingtime,stirringtime,andoilcupselection,asshowninFigure3-42.Therangefortheinitialsettlingtimeis0secondsto9minutesand59seconds,therangeforsettlingtimeis0secondsto9minutesand59seconds,andtherangeforstirringtimeis0secondsto99seconds.Thestatusofthethreeoilcupscanbeeither“selected”or“notselected”.Ⅱ.DielectricstrengthtestmethodforinsulatingoilFigure3-42

TestinstrumentparametersettinginterfaceⅡ.Dielectricstrengthtestmethodforinsulatingoil①Settlingtime:defaultvalueis15minutes,rangeis1to15minutes(increment=1minute).②Intervaltime:defaultvalueis5minutes,rangeis1to10minutes(increment=1minute).③Stirringtime:defaultvalueis10seconds,rangeis5to90seconds(increment=5seconds).④Stopvoltage:defaultvalueis80

kV,rangeis10to80

kV(increment=10

kV).Whentheinstrumentreachesthe“stopvoltage”,itwillstopincreasingvoltageandentertheholdstate.Ifnobreakdownoccursfor50seconds,theinstrumentwilldefaultthecurrentstopvoltageasthedielectricbreakdownvoltageoftheinsulatingoil.Ⅱ.Dielectricstrengthtestmethodforinsulatingoil⑤Numberofpressurecycles:defaultvalueis6times,optionalrangeis1to6times(increment=1time).Aftersetting,pressthe“confirm”buttontoreturntothestartpage,andpressthe“start”buttontobegintesting.(2)Select“starttest”andclick“run”tostartthetest.Theinstrumentwillcyclethroughthesequenceofincreasingvoltageuntilbreakdown,stirring,settling,andthenincreasingvoltageuntilbreakdownagainuntilthesetnumberoftestsisreachedandtheteststops.(3)Afterthebreakdowntestiscompleted,thedisplayscreenoftheinstrumentshowsthetestresults,includingbreakdownvoltageandaveragebreakdownvoltage,asshowninFigure3-43.(4)Theoperatorcanalsosaveandprintthetestresultsasneeded.Ⅱ.Dielectricstrengthtestmethodforinsulatingoil(Ⅱ)Theoperatingmethodofthewithstandvoltagetestisasfollows(1)Setthetestparameters,includingvoltage,withstandtime,andoilcupselection.(2)Select“starttest”andclick“run”.Theinstrumentwillincreasevoltageuntilitreachesthesetwithstandvoltage.Ifabreakdownoccursduringthevoltageincreaseprocess,thetestwillenddirectly.Ifnobreakdownoccursduringthevoltageincreaseprocessandtheinstrumentreachesthesetwithstandvoltage,itwillstayatthatvoltageforthedurationofthe“withstandtime”.(3)Afterthewithstandvoltagetestiscompleted,thedisplayedtestresultsincludethewithstandvoltage,withstandtime,andtestresult(OKforpassingorNOforfailing).Ⅱ.Dielectricstrengthtestmethodforinsulatingoil(4)Theoperatorcanalsosaveandprintthetestresultsasneeded.Thedisplayedcontentonthescreenincludesthetotalnumberofsavedtestgroups,theserialnumberofthecurrentlyselectedgroup,andthestoragetime.Theoperationforviewinghistoricaldataisasfollows:Movethecursortothe“confirm”buttontoenterthetestresultviewingscreen.ThetestresultscreenisshowninFigure3-43.Inthesescreens,choosetoprint,saveordeletethedataforthatgroup.Figure3-43

WithstandvoltagetestresultⅢ.InsulationoildielectricstrengthtestprecautionsDielectricstrengthtestingisquitesensitivetoslightcontaminationofthesample,anditiseasyforthesampletoabsorbmoistureduringsampling.Therefore,cleananddrysamplingtoolsshouldbeusedtostrictlyfollowthesamplingmethodforelectricaloilsampling.Thetestoilmustbeplacedinthelaboratoryforaperiodoftimewithoutdamagingtheoriginalstorageandsealingbeforeopeningthecoverfortestingwhentheoiltemperatureisclosetoroomtemperature(thearbitrationtestshouldbeperformedbetween15–20C).Beforeopeningthecover,gentlyshakethetestoiltomiximpuritiesevenly,butdonotproducebubbles.Ⅲ.Insulationoildielectricstrengthtestprecautions1.OilCupCleaningMethod(1)Useacleanclothtorepeatedlywipethesurfaceoftheelectrodeandtheelectroderod.(2)Adjusttheelectrodegapwithastandardgauge.(3)Cleanwithanhydrousethanolfor3–4times,thendrywithahairdryer.Finally,cleanwithatestoilsamplefor2–3times.2.CleaningClean,anduncontaminatedpairoftweezersoramagneticglas